The Caras Park requires a lot of logistical work in order to put on a show there. You have to deal with security issues (fencing and staff), ticketing is almost impossible, sound is limited due to limits by city ordinance, etc. It's not that promoters are worried about loosing money, it's just that logistically it's a nightmare to host a concert in Caras Park. It's almost impossible to make money off the venue through concert promoting.